Vehicle evaporative emissions control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. The fuel vapors may be stored in a fuel vapor canister, for example. In an effort to meet stringent federal emissions regulations, emission control systems may need to be intermittently diagnosed for the presence of leaks that could release fuel vapors to the atmosphere.
One method of testing for the presence of undesired evaporative emissions in an emission control system may include applying a vacuum to a fuel system and/or evaporative emissions that is otherwise sealed. An absence of gross undesired evaporative emissions may be indicated if a threshold vacuum is met. In some examples, the fuel system may be sealed subsequent to the threshold vacuum being reached, and an absence of non-gross undesired evaporative emissions may be indicated if a pressure bleed-up is less than a bleed-up threshold, or if a rate of pressure bleed-up is less than a bleed-up rate threshold. Failure to meet these criteria may indicate the presence of non-gross undesired evaporative emissions in the fuel system and/or evaporative emissions system. In some examples, an intake manifold vacuum may be used as the vacuum source applied to the emissions control system. However, hybrid-electric vehicles (HEVs) have limited engine run time, and may thus have limited opportunities to perform such a test. Further, in order to improve fuel efficiency, vehicles may be configured to operate with a low manifold vacuum, and may thus have limited opportunities with sufficient vacuum to perform such tests for undesired evaporative emissions.
Thus, to meet emissions regulations, such vehicles may include an on-board vacuum pump, which may be included in an evaporative leak check module (ELCM). The ELCM may be coupled to the evaporative emissions system, within a canister vent line, for example. The ELCM may thus supply the vacuum for appropriate leak tests. However, installing an ELCM in a vehicle is a relatively expensive manufacturing cost, which increases with a correlation to evaporative emissions system and fuel tank volume. Thus, it may be desirable to improve upon the methodology for evacuating the fuel system and/or evaporative emissions system, such that costs may be reduced. The inventors have herein recognized these issues.
Furthermore, there may be circumstances where the pressure bleed-up test for the presence or absence of non-gross undesired evaporative emissions may be adversely impacted due to environmental or vehicle operating conditions. Specifically, bleed-up may be influenced by ambient temperature, fuel temperature, etc., thus making interpretation of the results of such a test challenging. For example, if a fuel system is evacuated to a target of −8 InH2O, but due to fuel vaporization as a result of high ambient temperature, 2-3 InH2O of vacuum are lost, then the results of such a test may be inconclusive as it may be challenging to interpret whether the bleed-up is due to the presence of a source of undesired evaporative emissions, or due to fuel vaporization. The inventors have herein recognized these issues.
Still further, in applying vacuum to the fuel system and/or evaporative emissions system under conditions where the engine is not in operation, fuel vapor may be drawn into a fuel vapor canister. By adding fuel vapor to the fuel vapor canister, the potential for undesired bleed-through emissions may be increased. For example, if the canister is nearly saturated with fuel vapor, any additional fuel vapor may saturate the canister and may result in fuel vapor escaping from the canister to atmosphere. Thus, it may be desirable to conduct any test for the presence or absence of undesired evaporative emissions in such a fashion that the potential for bleed-emissions are not increased. The inventors have herein recognized such issues.
Thus, the inventors have herein developed systems and methods address the above-mentioned issues. In one example, a method comprises conducting a test for undesired evaporative emissions stemming from a fuel system of a vehicle via in a first operating mode, evacuating the fuel system to a variable vacuum level through an entirety of a fuel vapor canister configured to capture and store fuel vapors, and in a second operating mode, evacuating the fuel system to the variable vacuum level through a portion of the fuel vapor canister.
In this way, the test for undesired evaporative emissions may be conducted in an environmentally friendly fashion, where under certain conditions the fuel vapors are routed through the canister while in other conditions the fuel vapors are only routed through a portion of the canister.
In an example of the method, the method further comprises learning common routes traveled by the vehicle, where learned routes include one or more learned key-off events, and further includes an expected duration of the one or more learned key-off events, and wherein evacuating the fuel system in both the first operating mode and in the second operating mode is in response to a learned key-off event duration below a threshold key-off duration.
In one example of the method, the variable vacuum level in the first operating mode is a function of a loading state of the fuel vapor canister and fuel volatility, and the variable vacuum level in the second operating mode is a function of fuel volatility but independent of the loading state of the fuel vapor canister. Evacuating the fuel system in the first operating mode is via a vacuum pump positioned between the fuel vapor canister and atmosphere, and evacuating the fuel system in the second operating mode is via an engine.
In this way, the fuel system may be evacuated in an environmentally friendly fashion, and may further be conducted in such a way that the results of a pressure bleed-up portion of the test is not adversely impacted by fuel volatility.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.